1. Technical Field
The present disclosure relates to an abnormality detection device for a continuously variable transmission and a method of detecting abnormality of the continuously variable transmission.
2. Related Art
These days, continuously variable transmissions (CVT) such as a chain-type CVT or a belt-type CVT, which allow a gear ratio to be continuously changed, are widely in practical use. In general, such a continuously variable transmission has a forward and reverse switching mechanism for switching between forward rotation and reverse rotation of driving wheels (that is, forward motion and reverse motion of a vehicle) (see, for example, Japanese Unexamined Patent Application Publication (JP-A) No. 2013-24327).
The forward and reverse switching mechanism described in JP-A No. 2013-24327 mainly includes a double-pinion type planetary gear train, a forward clutch, and a reverse brake. The forward clutch is, for example, a multi-plate clutch and is set in an engaged state when supplied with clutch pressure. Similarly, the reverse brake is a multi-plate brake and is set in an engaged state when supplied with brake pressure. When the forward clutch is engaged and the reverse brake is released, a forward state is assumed in which rotation of the engine is directly transmitted to a primary pulley. On the other hand, when the forward clutch is released and the reverse brake is engaged, a reverse state is assumed in which rotation of the engine is reversed by a planetary gear train and is transmitted to the primary pulley.
In general, a continuously variable transmission including a forward and reverse switching mechanism is controlled by an electrical control device using a microcomputer, for example. Although it is extremely rare for such an electrical control device to have a failure, a fault might occur in the microcomputer, for example, a fault in a memory such as a RAM and a register (for example, written data and read data do not match), a fault in a logical operation circuit, and variation in clock signal might occur. In addition, an error in setting or writing ROM data (such as control data) might occur.
In the case where such a hardware failure or an error in setting ROM data occurs, for example, abnormality of a target clutch pressure may cause abnormality of the above-mentioned clutch pressure, the target clutch pressure being a control target value of the clutch pressure. For example, in the case where the target clutch pressure has an abnormal value and the clutch pressure is reduced, the driving force of the engine is not transmitted to the driving wheels against the intention of a driver, that is, the intention of keeping the vehicle moving, and thus the driver may not be able to drive the vehicle. In the case where such an abnormal condition occurs in a vehicle on a slope as an example, the vehicle may slide down. However, for example, determination as to the above-described abnormality of a target clutch pressure, in other words, reasonableness of a control value of the forward and reverse switching mechanism has not been considered.